With reference to FIG. 1, a conventional computed tomography (CT) scanner 100 generally includes a rotating gantry 101 rotatably supported by a stationary gantry 102. The rotating gantry 101 supports at least an x-ray tube 103, which emits radiation that traverses an examination region and a portion of an object or subject therein. A subject support 120 (FIG. 4) supports a subject or object in the examination region. The illustrated rotating gantry 101 also supports a detector array 105, which is located opposite the radiation source 103 across the examination region, and which detects radiation traversing the examination region. The detector array 105 generates a signal, which is reconstructed to generate volumetric image data. Scans are performed with the rotating gantry in a vertical non-tilted position (FIG. 1) or a tilted position.
As shown in FIGS. 1, 2, 3 and 4, with the illustrated CT scanner 100, the stationary gantry 102 includes a gantry base 104 (FIGS. 1, 2 and 4), which mounts (e.g., via four (4) to six (6) or other number of different points over the area of the base 104) to the examination room floor, side supports 106 (FIGS. 1, 2 and 4), which extend vertically upward from the gantry base 104 to a height near the center 110 of the examination region (FIG. 1), a tilt support 112 (FIGS. 1 and 4), such as ball or other bearings, which are located in the side supports 106 up at a height near the center 110 of the examination region such as at a center of gravity of the system (FIG. 1), and a tilt frame 114 (FIGS. 1 and 4), which includes a support frame 115 (FIGS. 1 and 3), which rotatably supports the rotating gantry 101.
With respect to FIGS. 1 and 4, the tilt frame 114 is configured to tilt, about the tilt support 112 along a tilt axis 118, which extends transversely from side support 106 to side support 106 at about the center 110 or alternatively the center of gravity of the system (FIG. 1) of the examination region. Tilting the tilt frame 114 as such tilts the rotating gantry 101 about the tilt axis 118. The tilt frame 114 and the rotating gantry 101 can tilt from a vertical (or non-tilt) position 402 to a back (tilted) position 404 (as shown in FIG. 4) and/or a forward (tilted) position (not shown). When tilted in the back position 404, a bottom portion 126 (FIG. 4) of the tilt frame 114 protrudes out past the gantry base 104 by a distance 128 such that a support base 122 of a subject support 120 has to be located at least the distance 128 away from the gantry base 104 to avoid a collision with a tilted tilt frame 114.
With the scanner 100 of FIG. 1, the gantry base 104 and side supports 106 form a generally “U” shaped assembly (FIGS. 1 and 2), with a relatively large lateral width 130 (FIG. 2) and the side supports 106 running up past the center 110 of the examination region (FIG. 1) and connecting to the outside of the tilt frame 114 and the support frame 115 (FIG. 1). As a consequence, the gantry base 104 (FIGS. 1, 2 and 4) and the support frame 115 (FIGS. 1 and 3), and hence the system 100, tend to be relatively large, heavy, and/or expensive. A high compliance design will produce undesirably tight constraints on the allowable rotating gantry imbalance, while lower compliance can be achieved by higher frame stiffness and tighter tolerances between the frame interfaces, which increases cost. More specifically, the lateral stiffness of traditional tilt designs has always been a challenge, and the inherent large stiffness in and about all axes except the tilting generally is desirable. In addition, tight floor flatness tolerances over the large area of the gantry base 104 are needed to constrain the amount of load or distortion imposed on the base support.
Floor flatness tolerance may be reduced by adding significant structure between the tilt support locations, which can increase cost. Furthermore, the friction of the bearings of the tilt support 112 leads to wear and torque variance. Moreover, the scannable range of the subject support 120 is defined by the extent a table top 124 of the subject support 120 travels through the examination region. A consequence of tilting the tilt frame 114 about the tilt axis 118 is that the scannable range is decreased by the distance 128 as the support base 122 has to be at least the distance 128 away from the gantry base 104 as discussed above, or, in the alternative, the table top 124 (including the carriage system with guidance, bearing, motion devices, etc.) length has to be increased to compensate for the loss of the scannable distance 128, which can increase the cost of the subject support 120, Moreover, the base 104 and table top 124 (including the carriage, etc.) should be stiff enough to accommodate a large overhung load while keeping deflection within a predetermined tolerance.